Brush



rec ss Patented Feb. 22, 1949 BRUSH Robert S. Her-wig, North Ar to Bendix Avia tion Corporation,

lington, N. J., assig-nor Teterboro,

N. J a corporation of Delaware No Drawing.

Application January 24, 1944, Serial No. 519,531

10 Claims. (Cl. 171-325) moisture conditions.

As is well known, rapid wear or dusting of vapor concentration per cubic foot, the rate of wear increases as the atmospheric pressure surrounding the brushes decreases.

When brush wear It is an object of my invention, therefore, to provide a brush, whereby both such optimum conditions for long wear may be obtained at high or low altitudes. v

Another object of my invention is to provide a novel graphite brush mix, whereby the brush may be so impregnated as to provide such beneficial conditions.

Another object of ing dusting at high altitudes.

Another object of my invention is to provide a. mixture for the manufacture of graphite so as to prevent excessive wear of the brush at high altitudes.

that for the same waterequal to approximately 7% ases thus liberated will It is also an object of my invention to provide a commutator brush particularly adapted for use on an aircraft, and including an inorganic moisture adsorbent composition, whereby moisture vaporsmay be adsorbed by the brush when the aircraft is at altitude levels having an atmosgeneral meanings of the terms in which the appended claims are expressed.

Specifically, as an example of my invention, a brush such as described may be readily formed by adding to a metal-graphite mixture, which may contain by weight 60% carbon and 40% copper, an amount of barium nitrate by weight of the metal-graphite mixture. The said ingredients may then be well mixed in any suitable manner and compressed or otherwise formed into a block of suitable size to form. the commutator brush. The mixture may then be baked at approximately 1,500 F. by suitable heating means for hygroscopic barium oxide (BaO). The nitrogen activate the graphite mixture so that upon removal of the same from the heat treatment, there is formed a porous block. The porosity of the metal graphite block,

oxide (BaO).

It has been found that the metal-graphite brush formed in the manner described has re- Ihe long life of such graphite brushes is believed to be attributable to the barium nitrate (Ba(NOs)z) belng converted to a porous hygro- FERENCE scopic barium oxide (BaO) during the heat or baking process. Also the liberation of nitrogen gases during the heat treatment activates the graphite mixture resulting in a porous block structure. Since barium oxide (BaO) is extremely hygroscopic, moisture vapors are adsorbed into the brush at low altitudes where free moisture is prevalent so as to serve as a moisture supply for preventing the dusting or wearing of the brush due to lack of moisture at the extremely high altitudes.

The residual moisture carried by the brush serves to catalyze the formation of cuprous oxide (CuzO) on the conventional copper commutator. As is well known cuprous oxide (Cu2O) when in contact with graphite becomes an excellent lubricant.

The porosity of the graphite increases the amount of water vapor that the brush would normally adsorb. The adsorbed water vapor is liberated at high altitude causing the brush to be cooled by evaporation and, further, escaping oxygen reduces the friction between the graphite and the copper commutator by oxidizing any raw copper surface. v

While barium oxide (BaO) is hydroscopic it is only's'lightly water soluble so that after a flight at high altitude the brush is regenerated when theplane again returns to a level where moisture vapors are more prevalent as at sea level.

2. An article comprising a porous graphite finc -and a mdisture adsorbent or calcium sulfate.

3. In a method for forming a mosture adsorbent article; the steps consisting in mixing dihydrate calcium sulfate in a porous metal graphite mixture including; copper and carbon, compressing said mixture, and then subjecting said mix- As another example of 'my' invention I have found that by adding calcium sulfate dihydrate (CaSOI..2l-IzO)- to a suitable metal graphite mixture and properly baking the same, similar superior wearing qualities may be obtained. Thus, for example, such a' graphite brush may be formed by adding to a metal graphite mixture 'containing by'weight 60% carbon and 40% copper an amount of calcium sulfate dihydrate (CaSOQHzO) equalto 7;% by weight of the i'metal-graphite mixture. The mixture may then 'becompre'ssedor otherwise formed into a block of'suitable size toform the desired commutator brush andbakd at a temperature of approximately 1,500 F. in a'manner well known in the art. The heat treatmentconverts the calcium sulfate dihydrate (CaSO4.2I-IzO to anhydrous calcium sulfate (08.604). The heat treatment causes the evaporation of the water; held by the calcium sulfate dihydrate (09.804.21-120) However, anhydrous calcium sulfate is highly adsorbent of moisture so that upon the graphite block being permitted ,to cool= and-the porous block being exposed to moisture carried by the atmosphere water vapor may be adsorbed by. the

hygroscopic anhydrous calcium sulfate. I

- Such water vapors areliberated by the latter brush at high altitudes together with oxygen vapors for preventing the dusting of the brush and further causes the formation of-an oxide film on the commutator as previously explained.

It has been found that through use of the foregoinginvention, the life of commutator brushes athigh altitudes -in aircraft electrical devices may be remarkably increased. A p

;It is to be understood, however, that the conditions of temperature, concentrations and ingredients disclosed hereinabove are not limitations of my inventiombut are to be considered merely as illustrative of the practice thereof, since the invention is not to be limited except by the appended claims.

What is claimed is:

L A brush for use on a copper commutator,

comprising, in combination, agr'aphi'te block'of ture to a temperature sufficient to evaporate water from the dihydrate calcium sulfate so as to form anhydrous calcium sulfate, whereby the same is conditioned for the adsorption of atmospheric moisture vapor.

4. In a method for forming a moisture adsorbent article; the steps consisting in mixing barium nitrate in a'metal graphite mixture including copper and carbon; compressing "said mixture, and then subjecting said mixture to a temperature sufiic'ient to release nitrogen gas from the barium nitrate and causethe formation of barium oxide, and passing such nitrogen gases through said mixture so as to'foi'm said graphite mixture into a porous structure, whereby the same is conditioned for the adsorption of atmospheric moisture vapor.

5. A mixture'ior forming a" moisture adsorbent gra hite article, comprising in a graphite mixture an ingredient including a hydrated metallic sulfate in which the water is releasable in a vaporous form in response to heat, nd said hydrated metallic sulfate being converted into arr-anhydrous form so as to function as a moisture adsorption agent bysuch release of said water vapor '6. An electrical current conducting brush comprising a block of porous material containing a mixture oi graphite and a hygroscopic barium oxide derived duri g the processing or said brush from barium nitrate, and said mixture having such a porosity as to adsorbmoisture under-high moisture conditions and retain such moisture for low moisture conditions so as to prevent the dusting of said brush at high altitudes. i

, Z. An electrical current conducting brush comprising a block: oi porousmaterial containinga mixture :0? st nh1 ...an a y o c p m t li oxide derived during the processing of saidb 'ush frombarium nitrate, and said mixture having sucha porosity as to adsorbmoisture under high moisture conditions andretain suchmoisture ior low moisture conditions so as to prevent thedust- A ing of said brush at high altitudes 8. An electrical current conducting brush comprising-a block of porous material'containing a mi t e. a h tea d ab groscopic um sulfate derived during the processing -,of said brush from a dihydrated calcium sulfate, and

said e. hav n h oros tv: to ads r moisture under high-moistureconditions-and retain such moisture; for ;low moisture conditions so as to preventthe dusting of said-brush at-high altitudes.-

9. In a methodior forminga moisture-adsorbent current conducting'brush; the steps consisting of adding to acarbon-copper mixture: ;a minor proportion of an inorganic-material, said inorganic material being a member of agroup consisting of barium nitrate and calciuni sulfate dihydrate, then compressing saidmixture into the "form of a block, baking said'block atafteinperature sufiicient to release a gaseous medium from v agn y-:

vita-oz;- mi L i; L lian o es I 6 the inorganic material and change said inorganic REFERENCES CITED material into a hygroscopic form, and passing said gaseous medium through said block so as to form g 312225;: iferences are of record m the said block into a porous structure, whereby the 5 UNITED STATES PATENTS pheric moisture vapor through capillary action. Number Name 10. The method defined lay claim 9 in which 556,651 Markey P-$1 the proportion of said inorganic material is equal 1,071,044 Gilson Aug. 26, 1913 to approximately seven per cent by weight of the 1,895,756 Fuller Jan. 31, 1933 carbon-copper mixture, and the baking temper- 10 2,361,220 Loftes Oct. 24, 1944 ature is approximately 1500 degrees Fahrenheit. FOREIGN PATENTS ROBERT s. HERWIG. Number Country Date 1 579,509 Great Britain Aug. 6. 1946 

